If the Knicks deal for Tracy McGrady by next Thursday’s NBA deadline, it will have to be a three-team trade, with Al Harrington headed to the Wizards, a source confirmed.

A source familiar with the situation said talks between the Rockets, Knicks and Wizards are continuing, but the source did not sound overly optimistic they would be able to get it done.

“It’s possible, but I would not say it’s likely,” the source said. “The good news is there are talks and it’s all being discussed.”

Another NBA source said, “I think there can be something there at some point, but I think it will be hard for all three teams to hit their goals.”

The Wizards are looking to break up their team and take on the expiring contracts of Harington and either Larry Hughes or Darko Milicic in order to shed forward Caron Butler and possibly center Brendan Haywood, whom the Rockets view as strong assets. But more pieces have to be added — the Knicks likely have to put in $3 million of Jim Dolan’s cash.

The Knicks and Rockets were unable to complete a deal because Houston general manager Darryl Morey asked for lottery pick Jordan Hill and Knicks president Donnie Walsh refused.

A Knicks source said Walsh visited McGrady recently in Chicago, where McGrady has been working out with trainer Tim Grover.

The Knicks have shopped Harrington, believing his defense and playmaking do not fit exactly into their system.

McGrady is their best option for the trading deadline. If the Rockets can’t trade him, there is hope they would look to buy out his contract. That would make him a free agent and the Knicks would pursue signing him.

The Knicks are unwilling to take back any player in a trade who does not have an expiring contract.

* Though Danilo Gallinari and Nate Robinson were scheduled to fly to Dallas today, Robinson tweeted last night that is concerned he will not make it because of storm-related flight cancellations. Gallinari is scheduled to play in the rookie-sophomore game tomorrow and the 3-point shooting contest on Saturday. Robinson is in the slam dunk contest on Saturday.

* David Lee will continue with the Team USA program after he was named yesterday as one of the 27 national team members.